Mercury is found in small quantities in fluid streams such as hydrocarbon or other gas and liquid streams. Arsenic may also be found in small quantities in hydrocarbon streams. Mercury, in addition to its toxicity, can cause failure of aluminium heat exchangers and other processing equipment. Therefore there is a need to efficiently remove these metals from fluid streams, preferably as early as possible in the process flowsheet.
U.S. Pat. No. 4,094,777 discloses the use of a pre-sulphided absorbent comprising copper sulphide for the absorption of mercury from a natural gas stream containing mercury. The sorbent Is prepared by mixing a copper compound such as powdered copper hydroxycarbonate (also known as basic copper carbonate) with a support or dispersion material, for example a cement, and forming extrudates or granules. Alternatively the sorbent is prepared by impregnation of a support, such as alumina spheres, with a solution of a soluble compound of copper such as copper nitrate. The copper compound in the granules, extrudates or support is sulphided using hydrogen sulphide or a solution of a sulphide in water or in an organic solvent.
Whereas combining particulate copper carbonate with a particulate support or cement provides an effective sorbent, a considerable proportion of the copper can remain unavailable within the resulting extrudate or granule. Copper is now an expensive metal and it is desirable to provide sorbents with lower levels of Cu that retain the high capacity for heavy metals observed with the granulated or extruded products. Impregnated materials, such as copper-nitrate impregnated materials can require high sulphiding temperatures, or the addition of silver compounds in order to be fully sulphided, both of which are undesirable.